Manufacture of chemically-pure soluble silicic acid.



B. SGHWERIN.

MANUFAUTURE 0F OHEMIGALLY PURE SOLUBLE SIL IGIG AOID.

APPLiOATION FILED APR.18,1914.

1,132,394, Patented Mar. 16, 1915.

%TATE% manna canton.

BOTHO SCHWERIN, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR TO ELEKTRO- OSMOSE A. G. (GRAF SCHWERIN GESELLSCHAFT), OF FRANm0RTONTHE-MAIN,

GERMANY, A CORPORATION.

MANUFACTURE OF CHEMICALLY-PUBE SOLUBLE SILIOIC ACID.

' Application filed Apri1l8, 1914-.

To all whom it may concern:

Be it known that I, BOTHO SCHWERIN, a i

subject of the German Emperor, and residing at Frankfort-on-the-Main, Germany, have invented certain new and useful improvements in the Manufacture of Ghemically-Pure Soluble Silicic'Acid, of which the following is a specification.

The methods hitherto known for making soluble silicic acid do not yield a chemically pure product and the silicic acid can be preserved for a short time only. By the present method there is obtained in a simple manner a chemically pure and permanent silicic acid.

The procedure is as follows: An alkali silicate solution of 5-10 per cent. strength is poured into a diaphragm cell or into the anodic compartment of a suitably constructed diaphragm apparatus. There may be advantageously used as an anode a perforated electrode lying closely against the in ner face of the diaphragm wall. The diaphragm thus made is placed in a vessel containing pure water, the cathode being preferably constructed of wire net and lying closely against the outer face of the wall of the cell. The use of electrodes lying closely against the diaphragm Wall, particularly for the positive pole, prevents the separation of amorphous silicic acid.

The preparation of silicic acid for medical purposes is carried out with anodes of platinum netting. For technical use on the other hand the operation may be conducted with a suitable lead-antimony anode While a brass wire netting may advantageously serve as cathode. When current is supplied to the electrodes the alkali migrates through the diaphragm into the cathode chamber while soluble silicic acid remains in the anode chamber. There is, however, a loss arising from the fact that this silicic acid also leaves the anode chamber. This fact is the result of the amphoteric character in a colloidal chemical sense generally exhibited by the silicic acid in the anode chamber, and when acid residues are present the silicic acid migrates through the diaphragm toward the cathode. This disadvantage may be avoided by choice of a suitable diaphragm. Thus it is possible to give the diaphragm such a potential that only the alkali migrates through it, the silicic acid remain- Spec ification of Letters Patent.

Patenteollliar. 316, 18*15. Serial No. 832,942. I

now completely free from alkali residues but still .contains'traces of acids which (like mineral acids and carbonic acid) are de- ,rived from the'manufacture of the alkali silicate. In order to separate these con stituents also the cathodic purification is succeeded by an anodic purification. The procedure may be as follows: The silicic acid is'introduced into a vessel serving as .CfillllOClQ, the anode being surrounded by a diaphragm which may consist advantageously of parchment paper. When current passes, the acid residues migrate through the diaphragm from the cathode chamber into the anode chamber, while the soluble silicic acid does not vary or move out of the, cathode chamber. Proportionally with the extent to which the acid residues wander. out the potential may be raised so that even the last traces of acid may be quickly separated. The silicic acid thus obtained is quite chemically pure and, when suitably stored, permanent.

In the drawing attached hereto, which is a vertical section of the apparatus which may be employed for carrying out the process disclosed herein, 1 indicates a vessel of any suitable form in which is mounted a cathode 2 surrounding a diaphragm 3 in which is located anode 4. In the use of this particular apparatus diaphragm or cup 3 receives the alkaline silicate and the vessel 1 is filled with Water. When the current is passed between the electrodes, the alkali goes through diaphragm 3 into the vessel 1, whereas the soluble silicic acid remains in the diaphragm or cell 3. If the silicic acid is free from traces of alkali this same apparatus may be employed for the anodic purification. For said anodic purification all that is required is to bring the silicic acid. purified as indicated above, into the vessel 1, the diaphragm 3 for this anodic tit") purification being made of a mixture of oarborundum andcorunduni as set forthin my Patent N 0. 1,027,004, already mentioned.

As the current is passed between the electrodes the silicic acid remaimng in the vessel 1 passes through the diaphragm, and-chemically pure soluble silicic acid, remains in the vessel 1. i

What I claim, is: e

The method of manufacturing chemically 15 phragm of such potential as will allow the migration therethrough of alkali but pre vent the migration of silicic acid, and in subsequently subjecting the silicic acid so obtained to the action of the electric current in a cathode compartment of a cell provided with a diaphragm of such potential as will admit of the migration therethrough of .acid residues, but prevent migration of the soluble silicic acid.

In testimony whereof I affix my signature in presence of two Witnesses.

'BOTH'O SCHWERIN. Witnesses: JE N Gianni), I TCARL GRUND. 7 

